Appropriate irradiation with sunlight provides beneficial effects for organisms, such as vitamin D synthesis and microbicidal action. However, excessive UV irradiation is extremely hazardous to skin.
For example, ultraviolet B (UVB) radiation with wavelengths ranging from 290 nm to 320 nm reaches the dermic layer of skin so as to damage the DNA of the subcutaneous tissue. Thus, long-time exposure to UVB causes alteration in collagen fibers, formation of wrinkled skin and sagging skin, and also causes pigmentation, such as pigmented spots and freckles. Moreover, skin cancer may be formed.
Furthermore, ultraviolet A (UVA) radiation with wavelengths ranging from 320 nm to 400 nm does not have any direct damaging action. However, UVA is thought to excite photosensitive substances so as to indirectly cause skin melanism (suntan) and the like.
In particular, advancing destruction of the ozone layer due to air pollution caused by, for example, Freon gas has led to recent drastic increases in the quantity of ultraviolet rays reaching the surface of the earth. Hence, protection against ultraviolet rays is an important issue.
To protect skin from ultraviolet rays, many external cosmetics and sunscreen agents have been conventionally developed. A sunscreen agent mainly comprises: an ultraviolet absorber that absorbs ultraviolet rays before they reach the inside of the skin so as to reduce ultraviolet rays reaching the inside of the skin and to protect skin and an agent for scattering ultraviolet rays that causes reflection or scattering of ultraviolet rays to which skin is exposed so as to reduce the quantity of ultraviolet rays reaching the inside of the skin. As an ultraviolet absorber, for example, benzophenone-based 2-hydroxy-4-methoxybenzophenone, p-aminobenzoic acid-based agents, methoxycinnamic acid-based p-methoxycinnamic acid-2-ethylhexyl, salicylic acid-based phenyl salicylate, or 4-tert-butyl-4′-methoxybenzoylmethane is used. Furthermore, as an agent for scattering ultraviolet rays, for example, titanium oxide or zinc oxide is used.
However, it has been indicated that the long-term use of these chemical substances or metals may have adverse effects on skin by, for example, stimulating skin.
Accordingly, a safe and secure means and/or method for protecting skin from damage due to ultraviolet rays have been desired.